staging: rtl8723bs: Fix spelling/grammar errors in comment.

Fix the spelling/grammar errors in the comment block describing
the 'Function' member of 'struct rt_firmware_hdr'.

Signed-off-by: Quytelda Kahja <quytelda@tamalin.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>