clk: gate: fix comment typo and grammar

Change ouput -> output.

While at it change also grammatically incorrect "it's" to "its".
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Link: https://lore.kernel.org/r/d47978a09dd0320f9929a19fa3e829608a02b224.1693485415.git.baruch@tkos.co.ilSigned-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/clk-gate.c

@@ -15,7 +15,7 @@
 #include <linux/string.h>
 
 /**
- * DOC: basic gatable clock which can gate and ungate it's ouput
+ * DOC: basic gatable clock which can gate and ungate its output
  *
  * Traits of this clock:
  * prepare - clk_(un)prepare only ensures parent is (un)prepared