[aacraid] Handle both AIF and SYNC interrupts

Without this change, if an AIF interrupt comes at the same time a SYNC
command is finished, the SYNC interrupt will be lost. This happens because
all interrupt bits (bellbits) are cleared, but only one of them is handled.

Debugging shows that, (at least) when !sc->msi_enabled and (sc->flags &
AAC_FLAGS_SYNC_MODE) is true (sync mode), both bits may be set at the same
time.

PR: 237463
Reviewed by: scottl
Sponsored by: Eldorado Research Institute (eldorado.org.br)
Differential Revision: https://reviews.freebsd.org/D23859