staging: axis-fifo: axis-fifo: Fix function naming in the documentation

staging: axis-fifo: axis-fifo: Fix function naming in the documentation

Fixes the following W=1 kernel build warning(s):

 drivers/staging/axis-fifo/axis-fifo.c:356: warning: expecting prototype for axis_fifo_write(). Prototype was for axis_fifo_read() instead

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jacob Feder <jacobsfeder@gmail.com>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210414181129.1628598-52-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>