rpmsg: char: Rename rpmsg_char_init to rpmsg_chrdev_init

To be coherent with the other functions which are prefixed by
rpmsg_chrdev, rename the rpmsg_char_init function.

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20210311140413.31725-2-arnaud.pouliquen@foss.st.com


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>