soc: ti: pruss: Fix pruss APIs

PRUSS APIs in pruss_driver.h produce lots of compilation errors when
CONFIG_TI_PRUSS is not set.

The errors and warnings,
warning: returning 'void *' from a function with return type 'int' makes
	integer from pointer without a cast [-Wint-conversion]
error: expected identifier or '(' before '{' token

Fix these warnings and errors by fixing the return type of pruss APIs as
well as removing the misplaced semicolon from pruss_cfg_xfr_enable()

Fixes: 0211cc1e ("soc: ti: pruss: Add helper functions to set GPI mode, MII_RT_event and XFR")
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Link: https://lore.kernel.org/r/20241220100508.1554309-2-danishanwar@ti.com


Signed-off-by: Nishanth Menon <nm@ti.com>