Input: synaptics-rmi4 - fix a locking bug in an error path

Lock f54->data_mutex when entering the function statement since jumping
to the 'error' label when checking report_size fails causes that mutex
to be unlocked.

This bug has been detected by the Clang thread-safety checker.

Fixes: 3a762dbd5347 ("[media] Input: synaptics-rmi4 - add support for F54 diagnostics")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://patch.msgid.link/20260223215118.2154194-16-bvanassche@acm.org
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>