Input: touchscreen - use sizeof(*pointer) instead of sizeof(type)

Input: touchscreen - use sizeof(*pointer) instead of sizeof(type)

It is preferred to use sizeof(*pointer) instead of sizeof(type)
due to the type of the variable can change and one needs not
change the former (unlike the latter).

The refactoring is mostly trivial except for "usbtouchscreen.c"
file. Here, in the "mtouch_alloc" and "nexio_alloc" functions,
it is necessary to use a variable with a predefined type instead
of the "usbtouch->priv" variable (void * type). This way, the
"sizeof" operator can now know the correct size. Moreover, we
need to set the "usbtouch->priv" pointer after the memory
allocation since now the "kmalloc" return value is not assigned
directly.

This patch has no effect on runtime behavior.

Signed-off-by: Erick Archer <erick.archer@outlook.com>
Link: https://lore.kernel.org/r/AS8PR02MB723708364CC0DF2EAAFEE5968BC42@AS8PR02MB7237.eurprd02.prod.outlook.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>