smartpqi: Remove stray declaration

pqisrc_is_firmware_feature_enabled shouldn't be declared inline in a
header, and then static inline in the .c function. Remove this stray
declartion from the header. gcc6 complains, but clang does not.

Sponsored by: Netflix

(cherry picked from commit eae2ef5a010366c673ad912cae23b426ebb9a8a2)