Fix vi build on Linux/macOS

[arichardson]

Summary

This absolute include causes a build failure on Linux for me:
.../cheri/freebsd/contrib/nvi/cl/../common/common.h:10:10: fatal error: '/usr/include/db.h' file not found
#include "/usr/include/db.h" /* Only include db1. */

This change patches the file to use #include <db.h> instead until a
solution has been found upstream. See also https://github.com/lichray/nvi2/issues/69

Test Plan

compiles now

head/contrib/nvi/common/common.h

 arm64/arm64/swtch.S             standard
 arm64/arm64/sys_machdep.c       standard
 arm64/arm64/trap.c              standard
 arm64/arm64/uio_machdep.c       standard
 arm64/arm64/uma_machdep.c       standard
 arm64/arm64/unwind.c            optional        ddb | kdtrace_hooks | stack
 arm64/arm64/vfp.c               standard
 arm64/arm64/vm_machdep.c        standard
-arm64/cavium/thunder_pcie.c     optional        soc_cavm_thunderx pci
-arm64/cavium/thunder_pcie_fdt.c optional        soc_cavm_thunderx pci fdt
-arm64/cavium/thunder_pcie_pem.c optional        soc_cavm_thunderx pci
-arm64/cavium/thunder_pcie_common.c      optional soc_cavm_thunderx pci
+arm64/cavium/thunder_pcie.c             optional        soc_cavm_thunderx pci
+arm64/cavium/thunder_pcie_fdt.c         optional        soc_cavm_thunderx pci fdt
+arm64/cavium/thunder_pcie_pem.c         optional        soc_cavm_thunderx pci
+arm64/cavium/thunder_pcie_pem_fdt.c     optional        soc_cavm_thunderx pci fdt
+arm64/cavium/thunder_pcie_common.c      optional        soc_cavm_thunderx pci
 arm64/cloudabi64/cloudabi64_sysvec.c    optional compat_cloudabi64
 crypto/blowfish/bf_enc.c        optional        crypto | ipsec
 crypto/des/des_enc.c            optional        crypto | ipsec | netsmb
 dev/acpica/acpi_if.m            optional        acpi
 dev/ahci/ahci_generic.c         optional ahci fdt
 dev/hwpmc/hwpmc_arm64.c         optional        hwpmc
 dev/hwpmc/hwpmc_arm64_md.c      optional        hwpmc
 dev/mmc/host/dwmmc.c            optional        dwmmc