if_bnxt: Correcting the firmware package version parsing logic

The firmware package version currently appears as "Unknown" through
the sysctl interface. The parsing logic for extracting the firmware
package version from the package log has been modified to ensure
compatibility with all controllers.

Reviewed by: imp
Approved by: imp
Differential revision: https://reviews.freebsd.org/D42950

(cherry picked from commit e436cb79666db3c8bb167d47ca9803c36013e32c)