usb: gadget: Convert use of __constant_cpu_to_le16 to cpu_to_le16

In big endian cases, macro cpu_to_le16 unfolds to __swab16 which
provides special case for constants. In little endian cases,
__constant_cpu_to_le16 and cpu_to_le16 expand directly to the
same expression. So, replace __constant_cpu_to_le16 with
cpu_to_le16 with the goal of getting rid of the definition of
__constant_cpu_to_le16 completely.

The semantic patch that performs this transformation is as follows:

@@expression x;@@

- __constant_cpu_to_le16(x)
+ cpu_to_le16(x)

Signed-off-by: Vaishali Thakkar <vthakkar1994@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>