Input: fix the input_event struct documentation

Fix the datatype of the value field of the input_event struct which is
signed instead of unsigned.

Signed-off-by: Maud Spierings <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

Documentation/input/input.rst

···
 	    struct timeval time;
 	    unsigned short type;
 	    unsigned short code;
-	    unsigned int value;
+	    int value;
     };
 
 ``time`` is the timestamp, it returns the time at which the event happened.