bus: mhi: ep: Use kcalloc() instead of kzalloc()

This is an effort to get rid of all multiplications from allocation
functions in order to prevent integer overflows [1].

Here the multiplication is obviously safe because the "event_rings"
member never can have a value greater than 255 (8 bits). This member
is set twice using always FIELD_GET:

mhi_cntrl->event_rings = FIELD_GET(MHICFG_NER_MASK, regval);
mhi_cntrl->event_rings = FIELD_GET(MHICFG_NER_MASK, regval);

And the MHICFG_NER_MASK macro defines the 8 bits mask that guarantees
a maximum value of 255.

However, using kcalloc() is more appropriate [1] and improves
readability. This patch has no effect on runtime behavior.

Link: https://github.com/KSPP/linux/issues/162 [1]
Link: https://www.kernel.org/doc/html/next/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Erick Archer <erick.archer@gmx.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20240128112722.4334-1-erick.archer@gmx.com
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>