net: thunderbolt: Fix sparse warnings in tbnet_check_frame() and tbnet_poll()

Fixes the following warnings when the driver is built with sparse
checks enabled:

main.c:767:47: warning: restricted __le32 degrades to integer
main.c:775:47: warning: restricted __le16 degrades to integer
main.c:776:44: warning: restricted __le16 degrades to integer
main.c:876:40: warning: incorrect type in assignment (different base types)
main.c:876:40:    expected restricted __le32 [usertype] frame_size
main.c:876:40:    got unsigned int [assigned] [usertype] frame_size
main.c:877:41: warning: incorrect type in assignment (different base types)
main.c:877:41:    expected restricted __le32 [usertype] frame_count
main.c:877:41:    got unsigned int [usertype]
main.c:878:41: warning: incorrect type in assignment (different base types)
main.c:878:41:    expected restricted __le16 [usertype] frame_index
main.c:878:41:    got unsigned short [usertype]
main.c:879:38: warning: incorrect type in assignment (different base types)
main.c:879:38:    expected restricted __le16 [usertype] frame_id
main.c:879:38:    got unsigned short [usertype]
main.c:880:62: warning: restricted __le32 degrades to integer
main.c:880:35: warning: restricted __le16 degrades to integer

No functional changes intended.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>