realtek: Fix typo in Kconfig prompt

As the symbol RTL930x shows, the bool enables the RTL930x platform, not
the RTL839x one.

Signed-off-by: Olliver Schinagl <[email protected]>
(slightly changed commit subject)
Signed-off-by: Christian Lamparter <[email protected]>

target/linux/realtek/patches-5.10/300-mips-add-rtl838x-platform.patch

@@ -49,7 +49,7 @@
 +	select SYS_SUPPORTS_MULTITHREADING
 +
 +config RTL930X
-+	bool "Realtek RTL839X based platforms"
++	bool "Realtek RTL930X based platforms"
 +	depends on RTL83XX
 +	select MIPS_CPU_SCACHE
 +	select CSRC_R4K