[SCSI] qla4xxx: Fix a Sparse warning message

Fix following message:-
drivers/scsi/qla4xxx/ql4_os.c:3266:5: error: symbol 'qla4xxx_post_aen_work' redeclared with different type (originally declared at drivers/scsi/qla4xxx/ql4_glbl.h:186) - incompatible argument 2 (different signedness)

Signed-off-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>