Remove char/string conversions in fstab processing

There a few char->string conversions between functions which handle
different parts of fstab line processing, but there are no uses of
string functions. Pass char arrays/pointers around instead.

Change-Id: I976a9a54ee8dcfb6194cadcac6a34e467602003b
diff --git a/partitions.hpp b/partitions.hpp
index aafc4d4..ab34ec2 100644
--- a/partitions.hpp
+++ b/partitions.hpp
@@ -95,7 +95,7 @@
 	void Setup_Data_Media();                                                  // Sets up a partition as a /data/media emulated storage partition
 
 private:
-	bool Process_Fstab_Line(string Line, bool Display_Error);                 // Processes a fstab line
+	bool Process_Fstab_Line(const char *fstab_line, bool Display_Error);      // Processes a fstab line
 	void Find_Actual_Block_Device();                                          // Determines the correct block device and stores it in Actual_Block_Device
 
 	void Apply_TW_Flag(const unsigned flag, const char* str, const bool val); // Apply custom twrp fstab flags