mptfusion: remove redundant kfree checks

Fixes the following smatch warnings:

  drivers/message/fusion/mptfc.c:529 mptfc_target_destroy() info:
    redundant null check on starget->hostdata calling kfree()

  drivers/message/fusion/mptspi.c:465 mptspi_target_destroy() info:
    redundant null check on starget->hostdata calling kfree()

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
Acked-by: Sreekanth Reddy <Sreekanth.Reddy@avagotech.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>