usb: gadget: fix misspelling of current function in string

Replace a misspelled function name by %s and then __func__.

This was done using Coccinelle, including the use of Levenshtein distance,
as proposed by Rasmus Villemoes.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Felipe Balbi <balbi@ti.com>