clk: renesas: r9a06g032: Fix memory leak in error path

clk: renesas: r9a06g032: Fix memory leak in error path

The current code uses of_iomap() to map registers but never calls
iounmap() on any error path after the mapping. This causes a memory
leak when probe fails after successful ioremap, for example when
of_clk_add_provider() or r9a06g032_add_clk_domain() fails.

Replace of_iomap() with devm_of_iomap() to automatically unmap the
region on probe failure. Update the error check accordingly to use
IS_ERR() and PTR_ERR() since devm_of_iomap() returns ERR_PTR on error.

Fixes: 4c3d88526eba ("clk: renesas: Renesas R9A06G032 clock driver")
Signed-off-by: Haotian Zhang <vulab@iscas.ac.cn>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20251030061603.1954-1-vulab@iscas.ac.cn
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>